I recently came across a quote in a book:
"All single factor models share the limitation that shifts in curve levels cause shifts in the package of vanilla options that are a good hedge for the Bermudan option".
As far as I can see, all models would require hedge rebalancing for the Bermudan when rates change.
I fail to see why in particular, a one factor model would imply a higher amount of rebalancing, which is what I think this statement implies. Can anyone interpret this statement better for me, or reason why in particular a one factor model is less robust?